Cramer believes there's a trend underway in the market that you should know about.

And the Mad Money host believes it's not only responsible for recent gains, but it could also explain why the stock market could have significant upside for some time to come.

In a nutshell, Cramer believes buyers are facing a stock shortage. Now that's not to say, stocks are decreasing in number or being consumed, somehow. It's simply that the Mad Money host believes fewer investors are interested in selling.

Adam Jeffery | CNBC

That's largely because pro investors are held to a benchmark that they need to outperform. And that outperformance is pretty important – it's what separates the best from the rest. It allows top pros to command higher salaries and bigger bonuses.

Currently, Cramer thinks there are big fund managers who are not outperforming – in fact, he thinks they may be lagging their benchmark because they stayed on the sidelines too long.

Cramer can almost hear those pros saying, "I am falling behind the averages. I am not keeping up with my benchmarks and I am not making enough money."

And, the only way to stem those issues, at least right now, is to buy more stock.

Of course, additional buying sends indexes even higher, which is why the market could continue it's advance into uncharted territory.

The virtuous spiral often continues for quite some time, until another catalyst enters the market. The phenomenon is known on Wall Street as a 'chase for performance.'

What's the bottom line?

"I believe there is a stock shortage out there," Cramer said. "Sellers who had been hanging in the wings for years and years are either done selling or have no more to give. In turn, market pros have to pay up, which in turn drives additional gains. The result? Buyers become rabid."